In order to enhance transmission efficiency and throughput of a terminal having poor channel status, among multiple terminals existing in a cell, standardization for signal transmission and CO-MIMO (cooperative-MIMO) through a relay or femto cell in a 802.16m or LTE(-A) has been carried out. Moreover, in addition to the method for supporting a terminal by using the base station or a relay or femto cell, which performs the same operation as the base station, as described above, research on Client Cooperation (CC) transmission, which transmits signals through a cooperation between terminals, is currently being carried out in the 802.16m or LTE(-A).
Unlike the relay or femto cell, which is described above, CC refers to transceiving (transmitting/receiving) of signals between terminals (or user equipments or stations) via direct communication and cooperatively transmitting the transceived signal(s) to the terminal or base station.
When a source terminal and a cooperative terminal are cooperatively transmitting a signal from a UL region to the base station via client cooperation (CC) transmission, a signal that is intended to transmit UL data of the cooperative terminal itself may be generated, even in case of a cooperative terminal transmitting UL data of the source terminal to the base station. In this case, while performing the client cooperation transmission, in order to transmit its own signal, the cooperative terminal shall perform a resource request for signal transmission to the base station, so as to receive resource allocation for the UL signal transmission from the base station.
However, in the current CC operation, in case the cooperative terminal seeks to transmit its own UL data, while performing the client cooperation transmission, the detailed procedure respective to a resource allocation method of such case has not yet been defined.
First of all, a resource allocation request procedure of a general (802.16m system) terminal (or user equipment) will hereinafter be briefly described.
FIG. 1 illustrates an uplink resource allocation procedure using a contention-based request method.
Referring to FIG. 1, among many regions allocated via uplink for a Bandwidth Request, the terminal transmits a randomly selected CDMA code to a randomly selected slot (S110).
If the base station recognized the CDMA code transmitted from the terminal, the base station uses a CDMA allocation information element (CDMA_Allocation_IE), so as to allocate a resource, which is intended to enable the terminal to transmit a bandwidth request message (S120).
After receiving information on an uplink resource for transmitting the bandwidth request message, the terminal transmits the bandwidth request message to the respective resource region. At this point, the terminal may use a bandwidth request header (BR header), and information related to the size, and so on, of the requested bandwidth is included in the header (S130).
If the bandwidth requested by the terminal is available, the base station allocated an uplink resource to the terminal (S140). Thereafter, the terminal transmits data to the allocated uplink resource (S150).
FIG. 2 illustrates an exemplary 3-step random access based bandwidth request procedure.
In a wideband wireless connection (or access) system, the terminal may use a 3-step or 5-step random access method. The 5-step random access method may be used independently from the 3-step random access method, and the 5-step random access method may be used as a fall-back mode for a case when a malfunction occurs in the 3-step random access method.
A terminal (or AMS: Advanced Mobile Station) transmits a Bandwidth Request preamble sequence and a Quick Access Message to the base station at a randomly (or arbitrarily) selected opportunity (S210). Herein, the Bandwidth Request preamble sequence may also be expressed as a bandwidth request code (BR code).
At this point, a Station ID, which correspond to uplink bandwidth request information, and a BR index, which indicates the size of the bandwidth request and the QoS, and so on, may be included in the Quick Access Message.
The base station may transmit a BR ACK A-MAP information element, which indicates the reception status of the BR preamble sequence and the Quick Access Message transmitted from each terminal, to the terminals in the form of broadcast/multicast transmission (S220).
Once the base station has successfully received the BR preamble sequence and the Quick Access Message, the base station allocates uplink resource to each terminal and transmits uplink resource allocation information to each terminal through a UL basic assignment (or allocation) A-MAP IE (S230).
The terminal may transmit uplink data to the base station through the allocated uplink transmission region. At this point, the terminal may transmit additional uplink bandwidth request information to the base station along with the uplink data (S240).
FIG. 3 illustrates an exemplary 5-step random access based bandwidth request procedure corresponding to a fall-back mode for a case when a malfunction occurs in the 3-step.
The terminal transmits a BR preamble sequence (or BR code), uplink bandwidth request information (Station ID), a BR index indicating a request size and QoS, and so on, to the base station by using the Quick Access Message (S310).
The base station may transmit the reception status of the BR preamble sequence and the Quick Access Message, which are transmitted from each terminal, to the terminals in the form of broadcast/multicast transmission through a BR ACK A-MAP information element (IE). However, it will be assumed that the BR preamble sequence has been successfully decoded, yet that an error has occurred in the Quick Access Message. Therefore, the BR ACK A-MAP IE indicates that the BR preamble sequence has been successfully received and that an error has occurred in the Quick Access Message (S320).
In case the base station has only successfully received the BR preamble sequence, which is transmitted from the terminal, the base station allocates an uplink resource, which enables the terminal to transmit a bandwidth request (BW-REQ) message, to the terminal through a CDMA allocation A-MAP information element (CDMA Allocation A-MAP IE) (S330). In step S330, the CDMA Allocation A-MAP IE may be transmitted to the terminal in the form of a grant for an independent BR.
The terminal transmits a BW-REQ message (e.g., independent BR header format) to the base station through the allocated region (S340).
After receiving the BW-REQ message, which is transmitted from the terminal, the base station allocates uplink resource to the terminal by using UL basic assignment (or allocation) A-MAP IE or a grant message for uplink data transmission (S350).
The terminal transmits UL data to the base station through the allocated uplink resource region. At this point, the terminal may transmit additional uplink bandwidth request information to the base station along with the uplink data (S360).
More specifically, FIG. 3 illustrates the 5-step random access method as a fall-back mode of the 3-step random access method shown in FIG. 2. However, a general 5-step method is different from that shown in FIG. 3 in that the terminal does not transmit any Quick Access Message in step S310. And, the remaining process steps may be directly used and performed as described in FIG. 3.